It seems to me that if you try to lead your life by reason, you end up as a skeptic. A skeptic, of course, can believe many things, but will regard all these beliefs as tenuous hypotheses which can be modified or rejected if some experiences or reasons come along which seriously challenge those beliefs or demonstrate their falsity. In other words, the beliefs are mere guesses which we hold onto until something better comes along.
The life of reason leads to skepticism because (this is my guess) reason just doesn’t have the power to tell us much about the world. Or at least I’ll say that’s true of our reason; maybe there’s some other sort of being with a larger capacity for reason who can discover lots of things. But we can’t learn much through reason. And a wealth of experience doesn’t help a whole bunch, since experience always has to be interpreted somehow, and there are always alternative interpretations which reason can’t rule out. E.g. — am I really in causal contact with the keys I’m tapping? Or are my experiences being generated by a matrix/evil demon/dream?
Reason can help us sort out which guesses seem to us to be more likely — given other guesses we’ve made. So, for example, I assume that science gives us a decent picture of how the world works, on the whole. And given that picture, I can’t see that there is any room for a human soul, or for an Intelligent Designer, or some guarantee of divine providence. So — given my guess that modern science is right — reason helps me reach the conclusion that these other guesses (soul, God, hope) are wrong. I’ll be the first to admit that my initial guess, in favor of science, could be wrong. But if it’s right, I think I can mount a pretty compelling argument against believing in those other things.
So I end up as a skeptic, not very confident about our ability to know anything for sure, but fairly confident in reason’s ability to sort out which “guess packages” fit together and which don’t. And I can’t see that reason can give us much more than that.